The invention concerns a process and an apparatus for the drying and preheating of coking coal in a single flight stream tube.
The drying and preheating of coking coal is currently carried out in single- or multi-step processes, most of which latter comprise two steps. A flight stream apparatus consists of an as a rule vertically standing flight stream tube and one or more subsequent cyclones, in which the separation of gas from solids is carried out. The heat carrier gas is generally prepared in a combustion chamber and mixed vapors which are fed back serve to delimit the temperature. In the pretreatment of coking coal, the first step is a removal of about 10% of the coal moisture; subsequently, there is commonly a preheating of the coal to about 200.degree. C. In a single-step apparatus, only a predrying of the coking coal can now be achieved; for preheating, in contrast, a further process step is required, for example, in a second flight stream tube.
From the so-called Cerchar-preheater it is known, for example, that in a first step the drying of the coking coal may be effected through the use of an entrained bed (a fluidized bed with goods throughput through an especially high turbulence gas speed). In a subsequent flight stream stage--a second step--the coal is then heated to the desired temperature over 200.degree. C.
According to the Precarbon-process it is further known that two flight stream tubes may be operated on the countercurrent principle: i.e., the drying is carried out with the cooler gas from the heating stage and the heating to 200.degree. C with the hotter gas coming directly from the combustion chamber.
Finally, there is also known a type of apparatus in which the heat carrier gas is introduced in two portions into a single flight stream tube: in the lower portion the cooler gas is introduced for the drying of the coking coal and at about half the height of the flight stream tube the hotter heat carrier gas is introduced for preheating the coking coal.
In principle, it would be possible to carry out the drying and preheating of the coking coal in a single-step flight stream tube; nonetheless, this is generally only possible with carrier gas temperatures which lie far above the permissible limit for thermal pretreatment. This is because it is necessary to take precautions not to minimize the coking capacity of the coal through this process.
A principal disadvantage of the known methods for the preheating of coal for coking is the common feature that the ground or milled input material is variously affected by the process in dependence upon the size of the grain. Thus it has been recognized that the drying as well as the preheating process are more rapid as the grain size decreases. As the customary grain size for the ground raw coal ranges from about 6 mm to 0.001 mm, the fine grain fraction of this spectrum is more intensively influenced by the heat treatment than is the middle- and large-grain component.